Diffuser for led light sources

ABSTRACT

An LED light source is described. The light source includes an LED and a diffuser. The LED emits a light having a dominant wavelength. The diffuser includes a filler material, which includes particles. The mean diameter of the particles is at least as large as the dominant wavelength of the light emitted by the LED. The particles are configured to scatter the light emitted by the LED.

FIELD OF THE INVENTION

The present invention relates to providing uniformly dispersed lightfrom a light emitting diode (LED) source and to the efficient removal ofthe heat generated by the LEDs, and more particularly, to the uniformdispersion of the light generated by LEDs in a light source withoutsubstantial light loss, in order to provide a uniform illuminationsurface, and to permit the LEDs to be run at higher power.

BACKGROUND OF THE INVENTION

An LED consists of a semiconductor junction, which emits light due to acurrent flowing through the junction. A white LED is typically made byusing a blue or ultraviolet LED die, and adding a plastic coat to it,the coat containing a phosphor. The phosphor is used to convert the blueor ultraviolet light emitted by the LED die to a spectrum of light thatmore or less closely resembles white light or blackbody radiation.

At first sight, it would seem that white LEDs should make an excellentreplacement for the traditional lighting sources. At equal power, theygive far more light output than do incandescent bulbs, or, what is thesame thing, they use much less power for equal light; and theiroperational life is orders of magnitude larger, namely, 10-100 thousandhours vs. 1-2 thousand hours. Similarly, their ultimate efficiency ishigher than that of fluorescent tubes, and their lifetime is alsosubstantially longer than that of fluorescent tubes.

However, LEDs have a number of drawbacks that have prevented them, sofar, from being widely adopted as traditional lighting sources. One ofthese is that LEDs are discrete sources of light. They produce intenselight within the beam of their output, but dim light outside of thatbeam. Using multiple LEDs does not fully alleviate this problem, asthere are then interference patterns in the light.

In the past, LEDs have had diffusers added to their shells or bodies tospread out the light from the LED as a solution to the point lightsource problem. Another method has been to roughen the surface of theLED package. Neither of these methods accomplishes uniform lightdistribution for an LED light source, and may lower luminous efficiency.Methods of accomplishing approximate angular uniformity may also involvepartially absorptive processes, further lowering luminous efficacy.

Another drawback with LEDs is that although LEDs require substantiallyless power for a given light output than do incandescent bulbs, it stilltakes many watts to generate adequate light for illumination. An LED,being a semiconductor, is nearly a point source of heat, and cannot beallowed to get hotter than a range of approximately 85-150° C. The LEDthus has a substantial heat problem.

One possible solution to this heat problem is to use a large metallicheat sink, attached to the LEDs. This heat sink would then extend outaway from the bulb, removing the heat from the LEDs. However, thissolution is undesirable, because the heat sink may make it difficult forthe light source to fit in to the desired form factor.

SUMMARY OF THE INVENTION

This invention has the object of developing a diffuser for LEDs, suchthat the above-described primary problems are effectively solved. Itaims at providing a diffuser that may be attached to an LED lightsource, the diffuser uniformly distributing the light over the surfaceof the light source with very little light loss, and also providing alarge surface area for heat dissipation. The apparatus includes a sealedpanel, preferentially formed of a plastic such as polycarbonate, and afiller material, preferentially formed of a fluid, plastic or gel. Thefluid, gel or plastic is designed to either contain, or itself form, asystem of Mie scatterers. Additionally, the fluid, gel or plastic isdesigned to be, or to contain, material that efficiently removes heatfrom the LEDs and conveys it to a suitable surface for removal.

In accordance with one embodiment, the sealed panel has a rectangularcross-section. The fluid, gel or plastic fills the panel toapproximately 70-99%, or as suitable to provide room for thermalexpansion. The panel may be built as an integral part of the LED lightsource assembly, or may be an add-on attached by any of severalwell-known methods.

In accordance with another embodiment, the fluid, gel or plastic may bedistributed in the sealed panel with a non-uniform spatial distribution.This may be used to generate light that is more intense in one directionthan another.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a view of a present state-of-the-art LED light source showingthe reason for its directionality of light output.

FIG. 2 is a cross-sectional view of light emitted from an LED having Miescattering from supra-wavelength particles.

FIG. 3 is a cross-sectional view of an LED light source showing thediffuser mounted in front of the LEDs.

FIG. 4 is a cross-sectional view of an LED light source showing adiffuser with non-uniform spatial distribution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

According to the design characteristics, a detailed description of thecurrent practice and preferred embodiments is given below.

FIG. 1 is a view of a present state-of-the-art LED light source 10showing the reason for its directionality of light output and theconstruction used for removing heat. As shown in FIG. 1, the LEDs 20 aremounted on a circuit board 30. Since said LEDs are point sources oflight, the light emitted from the said LED light source appearsconcentrated in beams. Said circuit board provides electricalinterconnects for the LEDs 20, and may also provide electricalisolation. Wires 50 come from the circuit board to power the LEDs from apower source (not shown). The circuit board 30 is mounted to a heatsink40, made of a low thermal-resistivity material, whose purpose is toprovide a low thermal-resistance path to the ambient for heat generatedby the LEDs 20. In the drawing, heatsink 40 has fins 42 protruding fromit, but any shape of heatsink may be used.

FIG. 2 shows a cross-sectional view of light emitted from an LED havingMie scattering from a plurality of supra-wavelength particles 70 and anequal scattering of each of the wavelengths 80 according to a furtherembodiment. Typically, the incoming light 60 will include a plurality ofwavelength components, including a wavelength 62 based on thelight-emitting material used within the LED. For example, in a typicalLED emission spectrum, the wavelength 62 emitted from the LEDcorresponding to the color blue will be approximately 410 to 450 nm. Asshown in FIG. 2, the incoming light 60 impinges on a dispersed set orplurality of particles 70 having an effective diameter 90, wherein theeffective diameter 90 is greater than a dominant wavelength 62 of lightemitted from the LED. The effective diameter 90 of the dispersedparticles 70 are preferably a size one to a few times larger than adominant wavelength 62 of the light emitting source. For example, for anLED producing a blue light, the dispersed set of particles 70 can bealumina trihydrate having a mean diameter of approximately 1.1 microns.It can be appreciated that any suitable particles having an effectivediameter 90, which is greater than the dominant wavelength 62 of theemitting light source or LED and creates Mie scattering can be used. Itcan be appreciated that the particles need not be spherical, or evenapproximately spherical, and that other shapes can be used such as diskor rod-shaped particles. This creates the condition for Mie scatteringof the incoming light 60, wherein each of the incoming wavelengths 62are scattered into an outgoing wavelength 80. The transmitted light oroutgoing wavelengths 80 are thus dispersed in directions relative to theincoming light 60, without significantly affecting the light intensity.

FIG. 3 is a cross-sectional view of an LED light source 10 showing thediffuser 90 mounted in front of the LEDs. As shown in FIG. 3, the LEDs20 are mounted on a circuit board 30, and have power wires 50 coming offto their power source, not shown. Placed in front of said LEDs is thediffuser panel 90. Said diffuser panel is shown as being form-fitted tothe LEDs 20 and circuit board 30, providing a low-thermal resistancepath for the heat both of said LEDs and for the heat of said LEDs beingtransferred to said circuit board. The heat conducted by the diffuserpanel 90 may be transferred to ambient by conduction and radiation fromthe emitting surface 92. The diffuser panel 90 also spreads out thelight from the LEDs 20, producing an approximately uniform light outputon the emitting surface 92. It can be appreciated that the diffuserpanel 90 need not be rectangular in cross-section, and that other shapessuch as disk can be used. It can also be appreciated that the diffuserpanel 90 need not have a flat emitting surface, and that other shapessuch as hemispherical can be used. It can also be appreciated that thediffuser panel 90 need not be form-fitted to the LEDs 20, but may simplybe placed in front of them.

As shown in FIG. 3, the LED light source 10 includes at least one LED, apanel 90 between the at least one LED 20 and a light emission surface ofthe light source, and a filler material 91 inside the panel 90 toscatter the light from the at least one LED 20. In accordance with oneembodiment, the filler material 91 is a poly(acrylamide) hydrogel havinga plurality of particles, which have been lightly coated with inorganicparticles, such as calcium carbonate.

In accordance with another embodiment, the LED light source 10 includesat least one LED 20, a panel between the at least one LED 20 and a lightemission surface of the light source 10, and a filler material 91 insidethe panel 90 to scatter the light from the at least one LED 20, whereinthe filler material 91 contains small Mie cells plus a second differentdensity component. In accordance with an embodiment, the filler material91 is comprised of a hydrocarbon-based oil, with said second differentdensity component being composed of water and a small amount of asurfactant. It can be appreciated that the filler material 91 iscomposed of components that are individually each transparent to light.

FIG. 4 is a cross-sectional view of an LED light source, not shown,showing a diffuser 90 with non-uniform spatial distribution. As shown inFIG. 4, the diffuser 90 has two rectangular areas 94 in which thedensity of the fluid, gel or plastic filler material is lower than inthe other areas 96 of said diffuser 90. The lower density fillermaterial areas 94 may be formed with discrete boxes formed within thediffuser 90, or may simply be modulation in the density of the materialused. The effect of the lower density filler material areas 94 is toproduce light from those areas that is more direct and intense than inthe other areas 96 of the diffuser 90. The other areas 96 produce a morediffuse and less intense light. It can be appreciated that the lowerdensity filler material areas 94 need not be rectangular, and may be ofother shapes such as circles and annuli. It can also be appreciated thatthe filler material may be of uniform density, and only the Miescatterers may be varied in density.

It will be apparent to those skilled in the art that variousmodifications and variation can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. An LED light source comprising: at least one LEDconfigured to emit a light, wherein the light has a dominant wavelength;a diffuser configured to receive the light emitted by the at least oneLED, wherein the diffuser comprises a filler material includingparticles, and wherein the mean diameter of the particles is at least aslarge as the dominant wavelength; and wherein the particles areconfigured to scatter the light emitted by the at least one LED.
 2. TheLED light source of claim 1, wherein: the diffuser comprises a firstarea with a first density of the filler material and a second area witha second density of the filler material; and the first density is notthe same as the second density.
 3. The LED light source of claim 1,wherein: the diffuser comprises a first area with a first density of theparticles and a second area with a second density of the particles; andthe first density is not the same as the second density.
 4. The LEDlight source of claim 1, wherein the filler material is a fluid.
 5. TheLED light source of claim 1, wherein the filler material is a gel. 6.The LED light source of claim 1, wherein the filler material is aplastic.
 7. The LED light source of claim 1, wherein the particlescomprise alumina trihydrate.
 8. The LED light source of claim 1, whereinthe at least one LED is a blue or ultraviolet LED without a phosphor,and the filler material contains at least one phosphor.
 9. The LED lightsource of claim 1, wherein the filler material is a hydrogel.
 10. TheLED light source of claim 1, wherein the particles have been coated withinorganic particles.
 11. An LED light source comprising: at least oneLED configured to emit a light, wherein the light has a dominantwavelength; a diffuser configured to receive the light emitted by the atleast one LED, wherein the diffuser comprises a poly(acrylamide)hydrogel including particles, and wherein the mean diameter of theparticles is at least as large as the dominant wavelength; and whereinthe particles are configured to scatter the light emitted by the atleast one LED.
 12. The LED light source of claim 11, wherein: thediffuser comprises a first area with a first density of the particlesand a second area with a second density of the particles; and the firstdensity is not the same as the second density.
 13. The LED light sourceof claim 11, wherein the particles comprise alumina trihydrate.
 14. TheLED light source of claim 11, wherein the at least one LED is a blue orultraviolet LED without a phosphor, and the poly(acrylamide) hydrogelcontains at least one phosphor.
 15. The LED light source of claim 11,wherein the particles have been coated with inorganic particles.
 16. AnLED light source comprising: at least one LED configured to emit alight, wherein the light has a dominant wavelength; a diffuserconfigured to receive the light emitted by the at least one LED, whereinthe diffuser comprises a hydrocarbon-based oil and particles, andwherein the mean diameter of the particles is at least as large as thedominant wavelength; and wherein the particles are configured to scatterthe light emitted by the at least one LED.
 17. The LED light source ofclaim 16, wherein the diffuser further comprises a surfactant.
 18. TheLED light source of claim 16, wherein: the diffuser comprises a firstarea with a first density of the hydrocarbon-based oil and a second areawith a second density of the hydrocarbon-based oil; and the firstdensity is not the same as the second density.
 19. The LED light sourceof claim 16, wherein: the diffuser comprises a first area with a firstdensity of the particles and a second area with a second density of theparticles; and the first density is not the same as the second density.